Got the gas bill today for our York 80%, YP8C100, VS, modulating, NG furnace. It's part of an 18 SEER DFHP system but we have been running it on emergency heat or NG for a couple months due to some HP to furnace switch over issues discussed in another thread. We had quite a cold spell with 17 days below average temps so I am trying to sort out whether it is more efficient than the old single stage, 80%, 88,000 Btu furnace. The bill for 34 days is quite a bit higher than any of the comparable periods for the last 5 years, 190 CCF this year versus 123 CCF for last year.
I figure that the new furnace must typically run at a much lower Btu rating. The previous furnace should have been about 80% * 88,000 or around 70,000 Btu. The new unit seems to run at a low level so I figure that it is closer to 50% (typical modulation level) * 80% * 100,000 or closer to 40,000 Btu. Sound reasonable?
The gas bill isn't very detailed but we keep usage records from previous bills. But to accurately compare usage doesn't one need degree days? Can't say I really know what that means but seems to me our bill at the last house included this statistic. Anybody know if there are actual statistics for given time periods for our specific NW Arkansas location (72704) that can be compared?